Cu-ni-mn-al alloys

ABSTRACT

Strength and hardness of a copper-nickel-aluminium-manganese alloy is improved where the alloy contains nickel in the range ≧21% to ≦26% by weight, aluminium in the range ≧2.1% to ≦3.2% by weight and the Ni:Al ratio is between 8 and 10 (in terms of wt %).

This invention relates to alloys and in particular to copper based alloys containing nickel and more preferably to copper-nickel-manganese-aluminium alloys (hereinafter Cu—Ni—Mn—Al alloys).

Cu—Ni—Mn—Al alloys are widely used in marine environments where resistance to corrosion and hydrogen embrittlement are highly desirable. One such commercially available alloy known as Marinel (registered trade mark) 220 contains 19% nickel, 1.8% aluminium and 5% manganese. This alloy has a 0.2% proof stress of 700 N/mm2, UTS (ultimate tensile strength) of 870 N/mm2, elongation of 15% and a hardness of 269 BHN.

For applications where high strength and wear are especially desirable, for example bearing applications in the aerospace industry, beryllium-copper alloys having a hardness exceeding 300 BHN are currently preferred to Cu—Ni—Mn—Al alloys. However, such beryllium-copper alloys possess a low ductility (elongation of about 3%) making them susceptible to fracture under high load in an unpredictable manner. This is undesirable for many applications where failure can have catastrophic results. Moreover, beryllium is highly toxic and a Cu—Ni—Mn—Al alloy having comparable properties to existing beryllium-copper alloys would be highly desirable.

Cu—Ni—Mn—Al alloys are environmentally friendly and it would be desirable to provide a Cu—Ni—Mn—Al alloy that combines high strength with an acceptable ductility such that fracture under high load can occur in a more predictable manner allowing potential failure to be identified by routine inspection before it occurs.

A method of producing a hardened copper base alloy containing from 10 to 30% (preferably 10 to 20%) nickel and from 1 to 5% aluminium with a balance, apart from impurities, of copper is disclosed in GB 1520721. Reference is made to the addition of other elements but no specific examples of alloys or their properties are given.

We have now found that a Cu—Ni—Mn—Al alloy can be obtained having improved properties capable of wider application in which the alloy contains more than 20% nickel and the ratio of nickel to aluminium in the alloy is carefully controlled within specific limits. In particular, we have found that a Cu—Ni—Mn—Al alloy can be produced that can be used for bearing applications where high strength and high hardness which result in resistance to wear are especially desirable.

The above aims and objections are broadly achieved by the provision of a Cu—Ni—Mn—Al alloy containing nickel in the range ≧21% to ≦26% by weight, aluminium in the range ≧2.1% to ≦3.2% by weight wherein the Ni:Al ratio is at least 6.5 and preferably is between 8 and 10 (in terms of wt %), more preferably between 9 and 10 and most preferably between 9 and 9.5

Cu—Ni—Mn—Al alloys according to the present invention have improved properties compared to existing Cu—Ni—Mn—Al alloys such as Marinel 220 that makes them particularly suitable for use place of beryllium-copper alloys in applications where high strength and hardness are required.

More especially, the Cu—Ni—Mn—Al alloys according to the present invention have increased strength and hardness compared to existing Cu—Ni—Mn—Al alloys such as Marinel 220, enabling the Cu—Ni—Mn—Al alloys of the present invention to be used in place of beryllium-copper alloys.

Furthermore, the increase in strength and hardness is accompanied by only a small reduction in ductility (elongation) with the result that the Cu—Ni—Mn—Al alloys of the present invention are less susceptible to failure in an unpredictable manner compared to beryllium-copper alloys.

Additionally, the Cu—Ni—Mn—Al alloys of the present invention are environmentally friendly compared to beryllium-copper alloys which pose health and safety risks due to the toxicity of beryllium.

Preferably, manganese is present in an amount of from 2.8 to 4.1% by weight.

Cu—Ni—Mn—Al alloys according to the invention may beneficially include iron, chromium and niobium, preferably in a total amount of from 2 to 3.1% by weight, and may also optionally include one or more of titanium, vanadium, silicon, tantalum or tungsten.

The strength of the invented Cu—Ni—Mn—Al alloys is understood to derive from the precipitation of nanometre-scale Ni₃Al (γ′) phases. By employing a Ni:Al ratio of at least 6.5 in terms of wt %, the formation Ni₃Al can proceed to completion leaving a proportion of nickel in solution in the copper matrix to effect solid solution hardening. We have found that a Ni:Al ratio of 8 to 10, preferably 8.5 to 9.5 and more preferably 9 to 9.5 produces an alloy with a particularly beneficial combination of strength, hardness and ductility.

Crystallographic measurements of the lattice parameters of Ni₃Al with the addition of various elements show that elements such as silicon and vanadium decrease the lattice constant and the elements iron, chromium, manganese, titanium, tantalum and tungsten increase the lattice constant.

Such changes in the lattice parameters produce the result that silicon and vanadium increase the strengthening effectiveness of Ni₃Al through coherency hardening and iron, chromium, manganese, titanium, tantalum and tungsten increase the strengthening effectiveness of Ni₃Al through order hardening.

Of all these elements, iron, chromium, manganese are the most effective in assisting the hardening properties of Ni₃ μl.

The invented Cu—Ni—Mn—Al alloys may have the composition given in Table 1. TABLE 1 % by weight Nickel 21.0-26.0 Aluminium 2.1-3.2 Manganese 2.8-4.1 Iron 0.4-1.5 Chromium 0.3-1.5 Niobium 0.7-1.2 Titanium 0.0-0.5 Tungsten 0.0-0.5 Tantalum 0.0-0.5 Silicon 0.0-0.5 Vanadium 0.0-0.5 Copper Remainder

Especially preferred alloys have the composition given in Table 2. TABLE 2 % by weight Nickel 21.5-24.0 Aluminium 2.2-2.5 Manganese 3.0-4.1 Iron 0.4-1.1 Chromium 0.3-1.4 Niobium 0.7-1.2 Copper Remainder

The following properties can be achieved when alloys according to the invention are subjected to thermomechanical processing (forging and/or hot rolling) in the temperature range 800° C. to 1000° C. followed by heat treatment in the temperature range 350° C. to 600° C.: Property Minimum value 0.2% Proof stress (N/mm²) ≧850 Tensile Strength (N/mm²) ≧1000  Elongation  ≧8% (5.65 √S₀) Hardness ≧280 (BHN)

Preferably the 0.2% proof stress is ≧850 (N/mm²) and the hardness is ≧300 BHN.

The invention will now be described in more detail with reference to the following examples.

EXAMPLE 1

Experimental melt compositions for Cu—Ni—Mn—Al alloys were prepared by conventional methods having the range of compositions given in TABLE 3 Fe + Cr + Melt Ni Al Mn Fe Cr Nb Si Ti Cu Ni:Al Nb AA 23.4 2.0 5.4 1.0 0.5 0.8 0.02 — Balance 11.70 2.3 AB 25.3 2.0 5.2 1.1 0.4 0.8 0.02 — Balance 12.65 2.3 BA 21.2 2.3 4.1 1.2 0.5 0.8 0.03 — Balance 9.20 2.5 BB 21.5 2.5 4.0 1.1 0.4 0.7 0.01 — Balance 8.60 2.2 BC 21.4 3.1 4.1 1.1 0.4 0.7 0.02 — Balance 6.90 2.2 BD 21.8 2.4 3.9 1.3 0.7 0.8 0.02 — Balance 9.10 2.8 BE 23.7 2.5 4.1 1.2 0.4 0.7 0.03 — Balance 9.50 2.3 BH 23.8 2.5 4.0 1.2 0.4 0.7 0.02 — Balance 9.50 2.3 BM 25.8 2.8 4.1 1.2 0.3 0.7 0.01 — Balance 9.20 2.2

The properties for each of the alloys from Table 3 following a production route to 2″ diameter bar, involving thermomechanical processing in the temperature range 800° C. to 1000° C. are given in Table 4 TABLE 4 Melt 0.2% Proof Stress (N/mm²) UTS (N/mm²) Elong (%) AA 788 1010 20.4 AB 803 1024 19.8 BA 840 1013 9.5 BB 819 1004 11.9 BC 880 1043 13.1 BD 902 1059 9 BE 820 1030 16.4 BH 805 1003 9.6 BM 810  992 9

The results show that the strength of alloys in which the Ni—Al ratio exceeds 10, ie alloys AA and AB is lower and the ductility higher than alloys having a Ni:Al ratio in the range 6.5 to 10, i.e alloys BA to BM.

Heat treatment to effect further precipitation hardening was carried out in the temperature range 350° C. to 600° C. for each of the alloys BA to BM. The results are given in Table 5 TABLE 5 Melt 0.2% Proof Stress (N/mm²) UTS (N/mm²) Elong (%) BHN BA 890 1052 13.5 282 BB 841 1034 14.3 293 BC 884 1065 15.5 285 BD 907 1074 10.4 311 BE 873 1075  9.0 311 BH 858 1047 12.1 285 BM 848 1024 10.0 285

Comparison of the properties of various grades of Be—Cu alloys with Cu—Ni—Mn—Al alloys with a nickel content of less than 20% (Marinel 220), a Ni:Al ratio higher than 10 (alloy AA) and a Ni—Al ratio between 9 and 9.5 (alloy BD) is shown in Table 6 TABLE 6 Marinel Be—Cu Be—Cu Be—Cu 220 AA BD AMS 4650 AMS 4535 AMS 4651 Ni < 20% Ni 23.4 Ni 21.8 Minimum Minimum Minimum Alloy Type Ni:Al > 10 Ni:Al 11.9 Ni:Al 9.2 Properties Properties Properties 0.2% Proof 720 788 907 966 931 1000 Stress (N/mm²) UTS (N/mm²) 890 1010 1074 1138  1159  1241 Elongation (%) 15.5 20.4 10.4  3  4  3 Hardness 269 277 311 335 323  340 (BHN)

The results show that the alloy BD having a composition according to the invention has a hardness of 311 BHN that is significantly higher than both Marinel 220 and alloy AA and is comparable with the hardness of the beryllium-copper alloys AMS 4650, AMS 4535 and AMS 4651.

The hardness of a material is a major contributor to its wear properties and the alloy BD would therefore be expected to possess wear properties not dissimilar to the beryllium-copper alloys.

In addition, the results show that the 0.2% proof stress and tensile strength of the alloy BD are comparable with that of the Be—Cu alloys AMS 4650, AMS 4535 and AMS 4651 while the elongation (ductility) is significantly improved.

The elongation (ductility) of a material is a major contributor to its performance under load and the alloy BD would therefore be expected to fracture in a more predictable manner than the Be—Cu alloys AMS 4650, AMS 4535 and AMS 4651 which have very low elongation (ductility).

EXAMPLE 2

Experimental melt compositions for Cu—Ni—Mn—Al alloys were prepared by conventional methods having the range of compositions given in Table 7 (all amounts being % by weight) TABLE 7 Melt Ni Al Mn Fe Cr Nb Si Ti Cu Ni:Al Fe + Cr + Nb CA 22.8 2.3 2.0 0.3 1.2 0.7 0.02 — Balance 9.9 2.2 CB 23.0 2.3 3.0 0.3 1.2 0.7 0.02 — Balance 10.0  2.2 CC 21.5 2.2 2.8 0.5 1.1 0.7 0.02 0.07 Balance 9.8 2.3 CD 22.1 2.5 3.1 0.5 1.4  1.20 0.02 — Balance 9.0 3.1 CE 21.9 2.4 3.0 0.4 1.4 1.2 0.02 0.07 Balance 9.1 3.0

These alloys have a higher chromium content and a lower iron content than the alloys shown in Table 3. CD and CE also have a higher niobium content and CC and CE also include titanium.

The alloys were then subjected to thermomechanical processing and heat treatment as in the previous example and the properties are given in Table 8. TABLE 8 Melt 0.2% Proof Stress (N/mm²) UTS (N/mm²) Elong (%) BHN  CA* — — — — CB 867 1044 11.0 302 CC 901 1022 11.0 293 CD 972 1080 10.0 302 CE 970 1088  8.0 285 *no figures available for CA due to the alloy being unforgeable.

The results again show that the Cu—Ni—Mn—Al alloys according to the invention have increased strength and hardness compared to known Cu—Ni—Mn—Al alloys.

The 0.2% proof stress is generally relied on by engineers as providing an accurate indication of the strength of an alloy and the above examples show that the 0.2% proof stress of alloys according to the invention is significantly higher than that of existing Cu—Ni—Mn—Al alloys as demonstrated by Table 9 which compares the alloys of the invention with the known Marinel 220 alloy from Table 6 TABLE 9 0.2% Proof Stress UTS Elong Melt (N/mm²) (N/mm²) (%) BHN Ni:Al Ni Al CD 972 1089 10.0 302 9.0 22.1 2.5 CE 970 1088  8.0 285 9.0 21.9 2.4 BD 907 1074 10.4 311 9.1 21.8 2.4 CC 901 1022 11.0 293 9.8 21.5 2.2 BA 890 1052 13.5 282 9.2 21.2 2.3 BC 884 1065 15.5 285 6.9 21.4 3.1 BE 873 1075  9.0 311 9.5 23.7 2.5 CB 867 1044 11.0 302 10.0  23.1 2.3 BH 858 1047 12.1 285 9.5 23.8 2.5 BM 848 1024 10.0 285 9.2 25.8 2.8 BB 841 1034 14.3 293 8.6 21.5 2.6 Mari- 720  869 15.5 269 10.6  19.0 1.8 nel 220

The results indicate that a significant improvement in properties is achieved compared to Marinel 220 with alloys possessing a Ni:Al ratio of between 9 and 10. Preferred alloys have a 0.2% proof stress of at least 900 (N/mm²). These include alloys CD, CE, BD, CC which have a nickel content of 21.5 to 22.1 and an aluminium content of 2.2 to 2.5.

In the above tables, the following test procedures were employed 0.2% proof stress BS EN 10002 Pt 1 2001 UTS BS EN 10002 Pt 1 2001 Elongation BS EN 10002 Pt 1 2001 Hardness BS EN ISO 6506-1:1999 

1. A Cu—Ni—Mn—Al alloy containing nickel in the range ≧21% to ≦26% by weight, aluminium in the range ≧2.1% to ≦3.2% by weight and which possesses a Ni:Al ratio of between 8 and 10 (in terms of wt %).
 2. The alloy of claim 1 further including iron, chromium and niobium.
 3. The alloy of claim 2 further including one or more of titanium, vanadium, silicon, tantalum or tungsten.
 4. A Cu—Ni—Mn—Al alloy having Ni:Al ratio of between 8 and 10 (in terms of wt %) and the composition (% by weight): Nickel 21.0-26.0 Aluminium 2.1-3.2 Manganese 2.8-4.1 Iron 0.4-1.5 Chromium 0.3-1.5 Niobium 0.7-1.2 Titanium 0.0-0.5 Tungsten 0.0-0.5 Tantalum 0.0-0.5 Silicon 0.0-0.5 Vanadium 0.0-0.5 Copper Remainder


5. The alloy according to claim 4 wherein the nickel, aluminium, and manganese are present in the following amounts (% by weight): Nickel 21.5-24.0 Aluminium 2.2-2.5 Manganese 3.0-4.1 Iron 0.4-1.1 Chromium 0.3-1.4 Niobium 0.7-1.2


6. The alloy according to claim 5 wherein the nickel, aluminium, and manganese are present in the following amounts (% by weight): Nickel 21.9-22.1 Aluminium 2.4-2.5 Manganese 3.0-3.1


7. The alloy according to claim 1 having the following properties after thermo-mechanical processing in the temperature range 800° C. to 1000° C. and heat treatment in the temperature range 350° C. to 600° C.: 0.2% Proof Stress  ≧850 N/mm² Tensile Strength ≧1000 N/mm² Elongation (5.65 √S₀)   ≧8% Hardness  ≧280 BHN


8. The alloy according to claim 7 wherein the 0.2% proof stress is ≧900 N/mm².
 9. The alloy according to claim 7 wherein the hardness is ≧300 BHN.
 10. The alloy according to claim 1 wherein the Ni:Al ratio is ≧9.
 11. (canceled)
 12. (canceled)
 13. The alloy according to claim 4 having the following properties after thermo-mechanical processing in the temperature range 800° C. to 1000° C. and heat treatment in the temperature range 350° C. to 600° C.: 0.2% Proof Stress  ≧850 N/mm² Tensile Strength ≧1000 N/mm² Elongation (5.65 √S₀)   ≧8% Hardness  ≧280 BHN


14. The alloy according to claim 13 wherein the 0.2% proof stress is ≧900 N/mm².
 15. The alloy according to claim 13 wherein the hardness is ≧300 BHN.
 16. The alloy according to claim 4 wherein the Ni:Al ratio is ≧9. 